Piezoelectric thin film element, manufacturing method thereof, and liquid ejecting head and liquid ejecting apparatus employing same

ABSTRACT

The present invention provides a piezoelectric thin film element with superior piezoelectric properties in which the condition of the crystal of the piezoelectric thin film is appropriately controlled, and a manufacturing method thereof, as well as a inkjet recording head, inkjet printer, or other liquid ejecting apparatus employing the same. The piezoelectric thin film element  40  comprises a top electrode  44,  a bottom electrode  42,  and a piezoelectric thin film  43  formed between the top electrode  44  and the bottom electrode  42,  wherein the piezoelectric thin film  43  is structured so as to comprise a first layer  431  located nearest to the bottom electrode and second layers ( 433 - 436 ) that are located nearer to the top electrode than the first layer and that each have a thickness greater than that of the first layer  431.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a piezoelectric thin filmelement, a manufacturing method thereof, and a liquid ejecting head andliquid ejecting apparatus employing the same, and more particularly to apiezoelectric thin film element or the like with superior piezoelectricproperties and productivity.

[0003] 2. Description of the Related Art

[0004] Piezoelectric thin film elements that employ piezoelectric thinfilms that contain crystals typified by PZT (lead zirconate titanate;Pb(Zr_(x)Ti_(1-x))O₃) have functions such as spontaneous polarization,high permittivity, electro-optic effects, piezoelectric effects, andpyroelectric effects, and are applied in extensive device development.

[0005] A piezoelectric thin film element is structured by sequentiallystacking a substrate, a diaphragm, a bottom electrode, a piezoelectricthin film, and a top electrode. Since piezoelectric properties of apiezoelectric thin film vary according to the condition of the crystal(such as the orientation of the crystal that makes up the film), thecondition of the crystal must be controlled when the piezoelectric thinfilm is formed.

[0006] Possible methods of forming a piezoelectric thin film includesputtering, sol-gel processes, CVD, laser ablation, and the like, butsol-gel processes, which form a film by sol application, drying,pyrolyzing and annealing, are superior for controlling the condition ofthe crystal.

[0007] Such piezoelectric thin films are known to have superiorpiezoelectric properties when comprising a PZT fine crystal film with ahigh degree of orientation.

[0008] In conventional practice, PZT crystal films composed of stackedmaterial comprising a plurality of thin layers have been suggested forobtaining a PZT fine crystal film.

[0009] However, using stacked material comprising a plurality of thinlayers for the PZT crystal film has disadvantages in that the number oflayers must be increased in order to obtain the desired thickness,increasing the number of processes for forming the layers and decreasingproductivity. Due to the increase in the number or processes for formingthe layers, there is also a possibility that chances will increase forcontaminants such as waste to get mixed inside the film, causing therisk of reduced reliability for the piezoelectric thin film element.

SUMMARY OF THE INVENTION

[0010] Therefore, an object of the present invention is to provide apiezoelectric thin film element with superior piezoelectric propertiesin which the condition of the crystal of the piezoelectric thin film isappropriately controlled and a manufacturing method thereof, as well asa liquid ejecting head and liquid ejecting apparatus that employ thesame.

[0011] As a result of extensive research, the inventor developed thepresent invention upon discovering that a piezoelectric thin filmelement with superior piezoelectric properties can be obtained withoutaffecting productivity or reliability by reducing the thickness duringannealing of a first layer located nearest to a bottom electrode, and byproviding a second layer whose thickness is greater than that of thefirst layer to a top electrode during annealing.

[0012] The piezoelectric thin film element according to the presentinvention comprises a top electrode, a bottom electrode, and apiezoelectric thin film formed between the top electrode and the bottomelectrode, wherein the piezoelectric thin film comprises a plurality oflayers, and the plurality of layers comprises a first layer locatednearest to the bottom electrode, and a second layer that is locatednearer to the top electrode than the first layer and that has athickness greater than that of the first layer. In the piezoelectricthin film element, the bottom electrode is patterned in a specificconfiguration on a diaphragm; the piezoelectric thin film is formed bothon the bottom electrode remained after the patterning and on thediaphragm from which the bottom electrode has been removed; and theportion of the piezoelectric thin film on the bottom electrode remainedafter the patterning has a greater number of layers than the portion onthe diaphragm from which the bottom electrode has been removed.

[0013] Using such a structure makes it possible to obtain apiezoelectric thin film element with superior piezoelectric propertieswithout affecting productivity or reliability.

[0014] The thickness of the first layer is preferably between 10 nm and100 nm, and is more preferably between 20 nm and 50 nm. Productivity,reliability, and piezoelectric properties can be more effectivelypreserved when the thickness of the first layer located nearest to thebottom electrode is within this range.

[0015] The thickness of the second layer is preferably between 100 nmand 300 nm, and is more preferably between 150 nm and 200 nm.Productivity, reliability, and piezoelectric properties can be moreeffectively preserved when the thickness of the second layer is withinthis range.

[0016] The thickness of the entire piezoelectric thin film is preferablybetween 0.5 μm and 1.5 μm.

[0017] The first layer is preferably composed of a PZT crystal having arhombohedral crystal structure and a lattice constant of 4.070 Å orless. Having such a crystal structure makes it possible to obtain betterpiezoelectric properties and to produce a superior piezoelectric thinfilm element.

[0018] The PZT crystal is preferably a crystal comprising a solidsolution of any one of the following groups: lead titanate and leadzirconate; lead titanate, lead zirconate and lead magnesium niobate;lead titanate, lead zirconate and lead zincate niobate; or leadtitanate, lead zirconate and lead nickelate niobate.

[0019] A degree of orientation in (100) plane of the PZT crystal ispreferably 70% or greater in the thickness direction of thepiezoelectric thin film. The (100) plane degree of orientation iscalculated from I(100)/ΣI(hkl) by analyzing the diffraction strength (I)obtained by wide-angle X-ray diffraction. ΣI(hkl) is the sum of all thediffraction strengths of the (100) plane, the (110) plane, and the (111)plane obtained using the CuKα line. Having such a crystal structuremakes it possible to obtain better piezoelectric properties and toproduce a superior piezoelectric thin film element.

[0020] In a preferred embodiment, the bottom electrode is patterned in aspecific configuration on a diaphragm, and the piezoelectric thin filmis formed both on the bottom electrode remained after the patterning andon the diaphragm from which the bottom electrode has been removed by thepatterning, such that the portion of the piezoelectric thin film locatedon the bottom electrode remained after the patterning has a greaternumber of layers than the portion located on the diaphragm from whichthe bottom electrode has been removed.

[0021] The liquid ejecting head according to the present inventioncomprises the above-mentioned piezoelectric thin film element as apiezoelectric actuator for ejecting liquid.

[0022] The liquid ejecting apparatus according to the present inventioncomprises the above-mentioned liquid ejecting head.

[0023] The method of manufacturing a piezoelectric thin film elementaccording to the present invention comprises the steps of forming abottom electrode on a substrate; forming a piezoelectric thin film onthe bottom electrode by a sol-gel process; and forming a top electrodeon the piezoelectric thin film. In this method, the step of forming thepiezoelectric thin film comprises the steps of (a) applying a sol ontothe bottom electrode and then performing drying and pyrolyzing to form afirst precursor layer; (b) annealing the first precursor layer byheating from the substrate side to form a first layer of thepiezoelectric thin film; (c) applying the sol onto the first layer andthen performing drying and pyrolyzing to form a second precursor layer;and (d) annealing the second precursor layer by heating from thesubstrate side to form a second layer whose thickness is greater thanthat of the first layer.

[0024] Reducing the thickness of the first precursor layer initiallyformed on the bottom electrode and reducing the thickness duringannealing makes it possible to appropriately anneal the first layer andto obtain a fine crystal film with a high (100) plane degree oforientation. Making the thickness of the second layer (which is formedabove the first layer) greater than the thickness of the first layerimproves productivity. Since each layer formed above the first layer isformed while being sequentially crystallized in accordance with thecondition of the crystal of the first layer having a fine crystalstructure, the layers form a thin film comprising fine crystals eventhough thickness during annealing is increased. Consequently, accordingto the present manufacturing method, a piezoelectric thin film elementwith superior piezoelectric properties can be obtained without affectingproductivity or reliability.

[0025] In the above-mentioned manufacturing method, the second precursorlayer is preferably formed by applying the sol onto the first layer andperforming drying and pyrolyzing, and then again applying the solthereon and performing drying and pyrolyzing.

[0026] Specifically, the first layer located nearest to the bottomelectrode is formed by a sequence of steps of sol application, drying,pyrolyzing and annealing. The second layer is formed on the first layerby repetition of sol application, drying and pyrolyzing to form thesecond precursor layer, and by annealing the second precursor layer.This makes it possible to manufacture a piezoelectric thin film elementwith superior piezoelectric properties without affecting productivity orreliability.

[0027] The above-mentioned manufacturing method preferably has anotherstep of forming a Ti thin film on the bottom electrode, wherein thefirst precursor layer is formed by applying the sol to the bottomelectrode via the Ti thin film and then performing drying andpyrolyzing.

[0028] The step of forming the piezoelectric thin film further comprisea step of patterning the first layer and the bottom electrode afterforming the first layer and before forming the second precursor layer.In this case, the second precursor layer is formed by applying the solboth onto the first layer remained after the patterning and onto thesubstrate from which the bottom electrode has been removed.

[0029] The above-mentioned manufacturing method further comprises a stepof forming a Ti thin film with a thickness of between 1 nm and 4 nm onthe patterned first layer before forming the second precursor layer.

[0030] The method of manufacturing the liquid ejecting head of thepresent invention comprises the steps of forming a piezoelectric thinfilm element by the above-mentioned methods, etching the substrate toform a pressure chamber, and forming a nozzle plate covering thepressure chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a perspective view of an example of an inkjet printer,which is a liquid ejecting apparatus of the present invention;

[0032]FIG. 2 is an exploded perspective view of an example of an inkjetrecording head, which is a liquid ejecting head of the presentinvention;

[0033]FIG. 3 is an enlarged cross-sectional view of a liquid ejectinghead according to a first embodiment of the present invention;

[0034]FIG. 4 is a cross-sectional view showing a production process of aliquid ejecting head according to the first embodiment;

[0035]FIG. 5 is a cross-sectional view showing the production process ofthe liquid ejecting head according to the first embodiment;

[0036]FIG. 6 is a cross-sectional view showing the production process ofthe liquid ejecting head according to the first embodiment;

[0037]FIG. 7A shows an enlarged plan view of a liquid ejecting head(inkjet recording head), which is a component of the piezoelectricapparatus according to a second embodiment, and FIG. 7B shows across-sectional view along the line i-i in FIG. 7A;

[0038]FIG. 8 is a cross-sectional view along the line ii-ii in FIG. 7A;

[0039]FIG. 9 is a cross-sectional schematic view showing themanufacturing method of a piezoelectric element and a liquid ejectinghead (inkjet recording head) of the second embodiment; and

[0040]FIG. 10 is a cross-sectional schematic view showing themanufacturing method of a piezoelectric element and a liquid ejectinghead (inkjet recording head) of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Embodiments of the present invention are described below withreference to the figures. The present invention is by no means limitedthereby.

Entire Structure of Inkjet Printer

[0042]FIG. 1 shows a perspective view of an example of an inkjetprinter, which is a liquid ejecting apparatus of the present invention.The printer comprises a main body 2, a tray 3, a release opening 4, andan operating button 9.

[0043] The main body 2 is the case of the printer, and comprises afeeding mechanism 6 positioned to be able to supply paper 5 from thetray 3, and disposed therein is an inkjet recording head 1, which is aliquid ejecting head, so as to be able to print on the paper 5. Acontrol circuit 8 is provided to the interior of the main body 2.

[0044] The tray 3 is structured so as to be able to supply the paper 5to the feeding mechanism 6 before printing, and the release opening 4 isan opening for releasing the paper 5 after printing is complete.

[0045] The inkjet recording head 1 comprises the piezoelectric thin filmelement according to the present invention, and is structured so as tobe able to ejecting ink or other liquid from the nozzle according to asignal Sh outputted from the control circuit 8.

[0046] The feeding mechanism 6 comprises a motor 600 and rollers 601 and602. The motor 600 rotates according to the signal Sh outputted from thecontrol circuit 8, this rotational force is transmitted to the rollers601 and 602, and the paper 5 set on the tray 3 is pulled in by therotations of the rollers 601 and 602 and is supplied to be printed bythe head 1.

[0047] The control circuit 8 comprises a CPU, ROM, RAM, an interfacecircuit, and the like (not shown). According to the printing informationsupplied from the computer via a connector (not shown), the controlcircuit 8 outputs a signal to the feeding mechanism 6 or a drivemechanism of the head 1.

Structure of Inkjet Recording Head

[0048]FIG. 2 shows an exploded perspective view of an example of aninkjet recording head, which is a liquid ejecting head of the presentinvention.

[0049] The head is composed of a nozzle plate 10, a pressure chambersubstrate 20, a diaphragm 30, a bottom electrode 42, a piezoelectricthin film 43, and a top electrode 44.

[0050] The pressure chamber substrate 20 comprises a pressure chamber21, a side wall 22, a reservoir 23, and a supplying opening 24. Byetching silicon or other substrate, the pressure chamber 21 is formed asa storage space for ejecting ink or other liquid. The side wall 22 isformed so as to partition off the pressure chamber 21. The reservoir 23functions as a common flow conduit for supplying ink to each pressurechamber 21 via the supplying opening 24.

[0051] The nozzle plate 10 is affixed to one side of the pressurechamber substrate 20 such that a nozzle 11 is disposed in a locationcorresponding to each pressure chamber 21 provided to the pressurechamber substrate 20.

[0052] The pressure chamber 21 and the nozzle 11 are structured to beconnected at a predetermined pitch. The nozzle pitch can be variablydesigned as needed according to printing accuracy, and may, for example,be set at 400 dpi (dots per inch).

[0053] The bottom electrode 42, the piezoelectric thin film 43, and thetop electrode 44 are provided to the top surface of the diaphragm 30 atpositions corresponding to each pressure chamber 21, and function as apiezoelectric actuator. An ink tank inlet 35 is provided to thediaphragm 30, which makes it possible to supply ink stored in the inktank (not shown) to the reservoir 23 of the pressure chamber substrate20.

Layer Structure of First Embodiment

[0054]FIG. 3 shows an enlarged cross-sectional view of a liquid ejectinghead according to a first embodiment of the present invention. As shownin FIG. 3, the piezoelectric thin film element 40 is structured bystacking the diaphragm 30 on top of the pressure chamber substrate 20with the nozzle plate 10, and sequentially stacking thereon the bottomelectrode 42, the seed Ti film 45, the piezoelectric thin film 43, andthe top electrode 44.

[0055] A silicon single crystal substrate with a thickness of 220 μm ispreferably used as the pressure chamber substrate 20.

[0056] Films of silicon dioxide, zirconium oxide, tantalum oxide,silicon nitride, aluminum oxide, and the like are suitable for thediaphragm 30. In particular, it is preferable to stack together an SiO₂film 31 having silicon dioxide (SiO₂) formed on the pressure chambersubstrate 20, and a ZrO₂ film 32 having zirconium oxide (ZrO₂) formed onthe SiO₂ film 31.

[0057] The bottom electrode 42 is preferably formed by a single layer ofiridium, a single layer of platinum, a single film layer of an alloy ofiridium and platinum; or a stacked configuration comprising iridiumlayer/platinum layer, platinum layer/iridium layer, or iridiumlayer/platinum layer/iridium layer.

[0058] A seed Ti film 45 is formed on the bottom electrode 42. Formingthe seed Ti film 45 makes it possible to control the orientation of thepiezoelectric thin film 43 formed thereon. The seed Ti film 45preferably has a thickness between 3 nm and 10 nm, and more preferably 5nm. It is also acceptable for the seed Ti film to be island shaped andnot to have uniform thickness.

[0059] An appropriate buffer layer of an ultra thin titanium film orchromium film or the like may be interposed between the diaphragm 30 andthe bottom electrode 42 in order to further improve adhesion between thetwo. A thickness of 10 nm or more but 20 nm or less is suitable for thetitanium thin film.

[0060] The piezoelectric thin film 43 is structured by stacking sixlayers: the first layer 431 located nearest to the bottom electrode, andlayers 432, 433, 434, 435, and 436 formed sequentially thereon towardthe top electrode. The thickness of the first layer 431 is preferablybetween 10 nm and 100 nm. The thickness of each of the layers 432-436are greater than that of the first layer 431, preferably between 100 nmand 300 nm. The entire thickness of the piezoelectric thin film 43 ispreferably between 0.5 μm and 1.5 μm.

[0061] The first layer 431 is preferably structured from a PZT crystalhaving a rhombohedral crystal structure with a lattice constant of 4.070Å or less. This PZT crystal also preferably has a degree of orientationin (100) plane of 70% or greater in the thickness direction of thepiezoelectric thin film.

[0062] The first layer 431 and the layers 432-436 preferably compriselead titanate (PbTiO₃), lead zirconate (PbZrO₃), lead zirconate titanate(Pb(Zr, Ti)O₃), lead lanthanum titanate ((Pb, La)TiO₃), lead magnesiumniobate (Pb(Mg, Nb)O₃), lead lanthanum zirconate titanate ((Pb, La)(Zr,Ti)O₃), lead magnesium niobate zirconium titanate (Pb(Zr, Ti)(Mg,Nb)O₃), or the like.

[0063] Particularly, the following solid solutions are preferred: leadtitanate (PbTiO₃) and lead zirconate (PbZrO₃); lead titanate (PbTiO₃),lead zirconate (PbZrO₃), and lead magnesium niobate (Pb(Mg, Nb)O₃); leadtitanate (PbTiO₃), lead zirconate (PbZrO₃), and lead zincate niobate(Pb(Zn, Nb)O₃); or lead titanate (PbTiO₃), lead zirconate (PbZrO₃), andlead nickelate niobate (Pb(Ni, Nb)O₃).

[0064] The top electrode 44 is not particularly limited so long as itconsists of conductive material capable of being used as a commonelectrode, and may, for example, be a single-layer film of Pt, RuO₂, Ir,IrO₂, or the like, or a stacked film of two or more layers consisting ofPt/Ti, Pt/Ti/TiN, Pt/TiN/Pt, Ti/Pt/Ti, TiN/Pt/TiN, Pt/Ti/TiN/Ti,RuO₂/TiN, IrO₂/Ir, IrO₂/TiN, or the like.

Printing Operation

[0065] Printing operation of the above-mentioned inkjet recording headis described below. When a drive signal is outputted from the controlcircuit, paper is fed by operation of the paper feeder to a positionwhere it can be printed on by the head. When an ejecting signal is notsupplied from the control circuit and drive voltage is not appliedbetween the bottom electrode and the top electrode of the piezoelectricelement, no variation occurs in the piezoelectric thin film layer.Pressure variations do not occur in a pressure chamber provided with apiezoelectric element to which an ejecting signal is not applied, and noink droplets are ejected from the nozzle.

[0066] When an ejecting signal is supplied from the control circuit anda predetermined drive voltage is applied between the bottom electrodeand the top electrode of the piezoelectric element, the piezoelectricthin film layer is deformed. The diaphragm bends greatly in a pressurechamber provided with a piezoelectric element to which an ejectingsignal is supplied. Therefore, pressure is instantaneously increased inthe pressure chamber and ink droplets are ejected from the nozzle. Anycharacters or graphics can be printed by individually supplying ejectingsignals to the piezoelectric element in a position corresponding tovisual data in the head.

Manufacturing Method of First Embodiment

[0067] Next, the steps for manufacturing the piezoelectric thin filmelement according to the first embodiment will be described withreference to FIGS. 4 through 6.

Step of Forming the Diaphragm

[0068] First, as shown in FIG. 4(A), an SiO₂ film 31 with a thickness ofabout 1 μm is formed on the pressure chamber substrate 20 consisting ofsilicon by thermal oxidation, CVD, or other film forming methods.

[0069] Next, as shown in FIG. 4(B), a barrier layer 32 comprising a ZrO₂film is formed on the SiO₂ film 31. Sol-gel processes, reactivesputtering by introduction of oxygen gas with zirconium as a target, RFsputtering with zirconium oxide as a target, thermal oxidation followingformation of a zirconium film by DC sputtering, ion implantation, andthe like are used as methods for forming the barrier layer 32.

Step of Forming Bottom Electrode

[0070] Next, as shown in FIG. 4(C), a bottom electrode 42 comprising Ptor the like is formed on the diaphragm. CVD, electron beam vapordeposition, sputtering, or other methods are used to form the bottomelectrode 42. For example, a platinum layer with a thickness of 200 nmis formed. Or, a platinum layer with a thickness of 100 nm is formed andthen an iridium layer with a thickness of 100 nm is formed thereon.

Step of Forming Seed Ti Film

[0071] Next, as shown in FIG. 4(D), a seed Ti film 45 is formed on thebottom electrode 42 using DC magnetron sputtering, CVD, vapordeposition, or other film forming methods. The thickness of the seed Tifilm 45 is preferably between 3 nm and 10 nm. This seed Ti filmpreferably has nonuniform thickness and is island-shaped.

Step of Forming Piezoelectric Thin Film

[0072] Next, as shown in FIG. 5(E-1) through (E-9), a piezoelectric thinfilm 43 is formed on the seed Ti film 45 by a sol-gel process. Thesol-gel process involves converting a hydrated complex of a metalhydroxide (sol) into gel by dehydration, and annealing the gel to forman inorganic oxide film. When a sol-gel process is used, the PZT crystalgrows upward from the side of the seed Ti film 45 provided to the bottomelectrode 42, allowing the orientation of the PZT crystal to beadequately controlled.

[0073] When the piezoelectric thin film 43 is formed using a sol-gelprocess, the sol is first prepared by using acid or the like tohydrolyze acetate compounds or alkoxides such as methoxides, ethoxides,propoxides, or butoxides of titanium, zirconium, lead, zinc, or othermetals.

[0074] Next, as shown in FIG. 5(E-1), the sol is applied on the seed Tifilm 45. Spin coating, dip coating, roll coating, bar coating,flexographic printing, screen printing, offset printing, or othermethods are used to apply the sol. After the sol is applied, it is driedfor a predetermined time period below a predetermined temperature, andthe sol solvent is evaporated. The drying temperature is preferablybetween 150° C. and 200° C., and the drying time is preferably between 5and 15 minutes. After drying, a first precursor layer 51 is formed bypyrolyzing for a predetermined amount of time at a predeterminedpyrolyzing temperature in atmospheric conditions. The pyrolyzingtemperature is preferably between 300° C. and 500° C. The pyrolyzingtime is preferably between 5 and 90 minutes. Organic materialcoordinated to the metal is dissociated from the metal by pyrolyzing, anoxidative reaction is initiated, and the organic material is scatteredinto the atmosphere.

[0075] Next, as shown in FIG. 5(E-2), the first precursor layer 51 isannealed by heating from the substrate side, and the layer iscrystallized, yielding the first layer 431. Since the thickness of thefirst precursor layer 431 is reduced and annealing is performed byheating from the substrate side, adequate annealing can be achieved, andit is possible to obtain the first layer 431 comprising a crystallizedfilm with a lattice constant of 4.070 Å or less and a (100) plane degreeof orientation of 70% or greater. The annealing temperature ispreferably between 600° C. and 800° C. Setting the annealing temperatureat 600° C. or greater makes it possible to obtain a piezoelectric thinfilm with superior piezoelectric properties, and at 800° C. or less itis possible to suppress diffusion of the lead and to prevent unnecessaryoxidation of the bottom electrode. RTA (Rapid Thermal Annealing)apparatus or diffusion furnace or the like is used for annealing.

[0076] Similarly, as shown in FIG. 5(E-3) and (E-4), the sol is appliedonto the first layer 431, and drying and pyrolyzing are sequentiallyconducted to yield a precursor layer 52, which is annealed to form alayer 432. Since the layer 432 is formed while being sequentiallycrystallized in accordance with the crystal condition of the first layer431 having a fine crystal structure, a fine crystal similar to the firstlayer 431 can be obtained.

[0077] Next, as shown in FIG. 5(E-5) and (E-6), the sol is applied ontothe layer 432, the layer is dried and pyrolyzed, the sol is againapplied thereon, and the resulting layer is dried and pyrolyzed to forma precursor layer 53, which is annealed by heating from the substrateside, yielding a layer 433. Similarly, as shown in FIG. 5(E-7) and(E-8), the steps of sol application, drying, and pyrolyzing are repeatedtwice to form a precursor layer 54, which is annealed by heating fromthe substrate side, yielding a layer 434. Similarly, as shown in FIG.5(E-9), layers 435 and 436 are sequentially formed. The layers 433through 436 are each formed with a thickness larger than that of thefirst layer 431. A piezoelectric thin film 43 having six layers is thusformed. The layers 433 through 436 each have a thickness greater thanthat of the first layer, but since they are formed while beingsequentially crystallized in accordance with the crystal condition ofthe lower layer having a fine crystal structure, a fine crystal similarto the first layer 431 can be obtained.

[0078] The present invention is not limited to the present embodiment,and it is acceptable to reduce the thickness of the precursor layer 51of the first layer 431 located nearest to the bottom electrode, as it isfor the second layer (the layers 433-436 are equivalent to the secondlayer in the present embodiment) to be obtained by annealing the secondprecursor layer, whose thickness is greater than that of the firstprecursor layer 51. Specifically, a layer obtained by annealing aprecursor layer whose thickness is less than that of the first precursorlayer 51 may be included above the first layer (between the first andsecond layers, or above the second layer). The present invention is notlimited to cases in which six layers are stacked in the above-describedmanner.

Step of Forming Top Electrode

[0079] As shown in FIG. 5(F), the top electrode 44 is formed on thepiezoelectric thin film 43 obtained as described above. For example, DCsputtering may be used to form a film of iridium with a thickness of 100nm.

Etching Step

[0080] Next, as shown in FIG. 6(A), the top electrode 44 is spin-coatedwith a resist and patterned by being exposed or developed at a locationat which the pressure chamber is to be formed. Using the remainingresist as a mask, the top electrode 44, the piezoelectric thin film 43,the seed Ti film 45, and the bottom electrode 42 are etched by ionmilling, dry etching, or other methods.

Step of Forming Pressure Chamber

[0081] Next, as shown in FIG. 6(B), an etching mask is provided to alocation at which the pressure chamber is to be formed, and the pressurechamber substrate 20 is etched to a pre-determined depth byparallel-plate reactive ion etching or other dry etching methods thatuse active gas, yielding a pressure chamber 21. The remaining portionthat was not dry-etched forms the side wall 22.

Step of Bonding the Nozzle Plate

[0082] Finally, as shown in FIG. 6(C), the nozzle plate 10 is bonded tothe pressure chamber substrate 20 using an adhesive agent. In theprocess, each nozzle 11 is positioned so as to be disposed correspondingto the spaces of the pressure chambers 21. The pressure chambersubstrate 20, to which the nozzle plate 10 is bonded, is attached to thecase (not shown), completing the inkjet recording head.

EMBODIMENT 1

[0083] A piezoelectric thin film element was manufactured according tothe manufacturing method of the present embodiment. Specifically, anSiO₂ film with a thickness of 1 μm was first formed by thermal oxidationon a pressure chamber substrate having a thickness of 200 μm andconsisting of silicon, and a ZrO₂ film with a thickness of 400 nm wasformed thereon by reactive sputtering. Next, a platinum film with athickness of 100 nm was formed by CVD, and an iridium film with athickness of 100 nm was then formed by CVD, yielding a bottom electrode.A seed Ti film with a thickness of 5 nm was then formed on the bottomelectrode by DC magnetron sputtering.

[0084] A two-component sol, comprising a mixed solution of PbTiO₃ andPbZrO₃, was prepared as a starting material for the PZT film.

[0085] The sol was applied in a thickness of 10 nm by spin coating at1500 rpm to the seed Ti film. The coated film was dried for 10 minutesat 180° C. and then pyrolyzed for 60 minutes at 400° C., yielding afirst precursor layer. This first precursor layer was annealed andcrystallized by heating from the substrate side for 5 minutes at anannealing temperature of 650° C., yielding a first layer.

[0086] Next, the sol was applied in a thickness of 100 nm by spincoating at 1500 rpm, and the coating was dried, pyrolyzed, and annealedas described above.

[0087] Next, the sol was applied in a thickness of 100 nm by spincoating at 1500 rpm, and the coating was dried, pyrolyzed, and annealedas described above. The sol was then applied again in a thickness of 100nm by spin coating at 1500 rpm, the coating was dried and pyrolyzed asdescribed above, and the precursor layer was annealed by heating fromthe substrate side for 5 minutes at an annealing temperature of 650° C.These steps were repeated four times, yielding a piezoelectric thin filmhaving six layers, wherein the combined thickness of the six layers was1.0 μm.

[0088] Next, a film of iridium was formed on the piezoelectric thin filmby DC sputtering, yielding a top electrode with a thickness of 100 nm.

[0089] In the piezoelectric thin film element obtained as previouslydescribed, the first layer had a rhombohedral crystalline structure witha lattice constant of 4.068 Å. The degree of orientation in (100) planein the thickness direction of the first layer was 75%, so theorientation was predominantly along the (100) plane. Furthermore, thepiezoelectric constant of the obtained piezoelectric thin film elementwas measured, and it was found that the piezoelectric constant at 25 Vwas 152 pC/N, yielding favorable piezoelectric properties.

COMPARATIVE EXAMPLE

[0090] Except for obtaining a piezoelectric thin film having fivelayers, a piezoelectric thin film element was obtained in the samemanner as is embodiment 1. Specifically, in the comparative example, thesol was applied in a thickness of 100 nm by spin coating at 1500 rpm,dried for 10 minutes at 180° C., and pyrolyzed for 60 minutes at 400° C.The sol was then applied again in a thickness of 100 nm by spin coatingunder the same conditions, the coating was dried and pyrolyzed in thesame manner, and the precursor layer was annealed by heating from thesubstrate side for 5 minutes at an annealing temperature of 650° C.

[0091] These steps were repeated five times, yielding a piezoelectricthin film having five layers, wherein the combined thickness of the fivelayers was 1.0 μm.

[0092] In the piezoelectric thin film element obtained as describedabove, the layer located nearest to the bottom electrode had arhombohedral crystalline structure with a lattice constant of 4.072 Å.The degree of orientation in the (100) plane was 65% in the thicknessdirection of the layer. Furthermore, the piezoelectric constant of thepiezoelectric thin film element at 25 V was 132 pC/N.

[0093] It can be seen by the above results that the piezoelectric thinfilm element in Example 1 had, in comparison with the comparativeexample, a fine crystalline structure with a smaller lattice constantfor the first layer and a higher (100) plane degree of orientation, andhad superior piezoelectric properties as an element.

Structure of Second Embodiment

[0094]FIG. 7A shows an enlarged plan view of a liquid ejecting head(inkjet recording head), which is a component of the piezoelectricapparatus according to a second embodiment. FIG. 7B shows across-sectional view along the line i-i in FIG. 7A. FIG. 8 is across-sectional view along the line ii-ii in FIG. 7A. Identical symbolsare used to denote components similar to those in the first embodimentand the explanations thereof are omitted.

[0095] As shown in these figures, the piezoelectric element isstructured by sequentially stacking the ZrO₂ film 32, the bottomelectrode 42, the piezoelectric thin film 43, and the top electrode 44on the insulating film 31. An illustration of the seed Ti film 45 isomitted.

[0096] The bottom electrode 42 functions as a common electrode for eachpiezoelectric element. By contrast, a wiring bottom electrode 42 a isplaced on a layer of the same height as the bottom electrode 42, but isseparated from the bottom electrode 42 or other wiring bottom electrodes42 a, and is capable of conduction with the top electrode 44 via a stripelectrode 46. The piezoelectric thin film 43 has a portion formed on thebottom electrode 42 and another portion formed on the exposed diaphragm30 (on the ZrO₂ film 32) from which the bottom electrode 42 has beenremoved by patterning.

[0097] To obtain favorable piezoelectric properties, the portion of thepiezoelectric thin film 43 formed on the bottom electrode 42 shouldpreferably have a 100 plane degree of orientation (measured bywide-angle X-ray diffraction) of between 70% and 100%, and morepreferably of 80% or greater. Preferably, the 110 plane degree oforientation is 10% or less, and the 111 plane degree of orientationaccounts for the remainder. The sum of the 100 plane degree oforientation, the 110 plane degree of orientation, and the 111 planedegree of orientation is equal to 100%.

Manufacturing Method of Second Embodiment

[0098] Next, the method for manufacturing a piezoelectric elementaccording to the second embodiment is described. FIGS. 9 and 10 arecross-sectional schematic views showing the method for manufacturing apiezoelectric element and a liquid ejecting head (inkjet recording head)of the second embodiment.

Step for Forming the Diaphragm (S1)

[0099] An insulating film 31 is formed on a silicon substrate thatfunctions as the pressure chamber substrate 20. The thickness of thesilicon substrate may, for example, be about 200 μm. To manufacture theinsulating film, a high-temperature treatment is performed in anoxidizing atmosphere containing water vapor or oxygen, yielding asilicon dioxide (SiO₂) film with a thickness of, for example, 1 μm. Inaddition to the commonly used thermal oxidation, CVD can also be used.

[0100] Furthermore, a ZrO₂ film 32 with a thickness of 400 nm is formedon the insulating film 31. The ZrO₂ film 32 is obtained by performing ahigh-temperature treatment in an oxidizing atmosphere on the film formedfrom a Zr layer by sputtering, vacuum deposition, or other methods.

Step for Forming Bottom Electrode (S2)

[0101] Next, a bottom electrode 42 is formed on the ZrO₂ film 32. Thebottom electrode 42 is formed by a series of steps for forming, forexample, an Ir-containing third layer; forming a Pt-containing secondlayer on the third layer; and forming an Ir-containing first layer onthe second layer.

[0102] The above-mentioned first through third layers are formed bydepositing Ir or Pt on the ZrO₂ film 32 by sputtering or the like.Before the bottom electrode 42 is formed, an adhesive layer (not shown)comprising titanium or chromium may be formed by sputtering, vacuumdeposition, or other methods.

[0103] After the bottom electrode 42 is formed, a Ti layer (nucleus)should preferably be formed in succession on the bottom electrode 42.The Ti layer is formed in a thickness of between 3 nm and 20 nm bysputtering, for example. The Ti layer is formed uniformly over thebottom electrode 42, but it is acceptable to adopt an island shape insome cases.

First Step of Forming Piezoelectric Film (S3)

[0104] Next, a piezoelectric film is formed on the bottom electrode 42.In the first step, a first piezoelectric film layer 43 a is formed in athickness less than the desired thickness of the piezoelectric film 43,and preferably less than half the desired thickness thereof. Forexample, when the piezoelectric film 43 is composed of six layers in acombined thickness of 1.2 μm, the first piezoelectric film layer 43 acomprising at least one layer is formed in a thickness of 0.01 μmthrough 0.1 μm in the first step.

[0105] Specifically, a piezoelectric precursor film is formed by asol-gel process. A sol comprising an organic metal alkoxide solution isapplied onto the bottom electrode by spin coating or other coatingmethods. The coating is then dried at a predetermined temperature for apredetermined time, and the solvent is evaporated. After drying,pyrolyzing is performed at a predetermined temperature for apredetermined time in atmospheric conditions, and organic ligandscoordinated to the metal are thermally decomposed to yield a metallicoxide. The piezoelectric precursor film is stacked by repeating thesteps of coating, drying, and pyrolyzing a predetermined number oftimes; for example, twice. As a result of this drying and pyrolyzingtreatment, the metal alkoxides and the acetates in the solution form anetwork of metal, oxygen, and metal after the ligands are thermallydecomposed.

[0106] Next, the piezoelectric precursor film is crystallized byannealing. As a result of annealing, the piezoelectric precursor filmassumes a rhombohedral crystalline structure from an amorphous shape,and is converted to a film exhibiting electromechanical conversionaction. The first piezoelectric film layer 43 a consisting of a singlelayer is obtained by forming the above-mentioned piezoelectric precursorfilm and performing a single annealing step.

[0107] The first piezoelectric film layer 43 a thus formed is affectedby the composition of the bottom electrode 42 and the above-mentioned Tilayer, and the 100 plane degree of orientation is measured at 80% bywide-angle X-ray diffraction. As in the first embodiment, the thicknessof the first piezoelectric film layer 43 a is less than the thickness ofthe second layer, so adequate annealing can be achieved, and it ispossible to obtain a fine crystalline structure with a lattice constantof 4.070 Å or less.

[0108] According to the above-mentioned annealing, part of the bottomelectrode 42 is oxidized, and the thickness thereof is increased bydiffusing part of the PZT components. In the method in which thepiezoelectric film is formed after the bottom electrode has beenpatterned, the increase of the thickness of the bottom electrode nearthe patterning boundaries is less than in other portions, and thethickness is therefore not uniform, but since the first piezoelectricfilm layer 43 a is formed before the bottom electrode 42 is patterned inaccordance with the method of the present embodiment, the entirethickness of the bottom electrode increases and while remaining uniform.

Step for Patterning Bottom Electrode and Piezoelectric Film (S4)

[0109] Next, the first piezoelectric film layer 43 a is masked in thedesired configuration, the first piezoelectric film layer 43 a and thebottom electrode 42 are patterned by etching the periphery thereof, andthe wiring bottom electrode 42 a is separated from the bottom electrode42. Specifically, a resist material of uniform thickness is firstapplied (not shown) onto the first piezoelectric film layer 43 a byspinning, spraying, or other methods, and a resist pattern is thenformed (not shown) on the piezoelectric film by exposure or developmentafter the mask is formed into a specific configuration. The firstpiezoelectric film layer 43 a and the bottom electrode 42 are etched outby ion etching, dry etching, or other commonly used methods, exposingthe ZrO₂ film 32.

[0110] Next, a Ti layer (nucleus) is formed on the first piezoelectricfilm layer 43 a and the ZrO₂ film 32 by sputtering or other methods. TheTi layer preferably has a thickness of between 1 nm and 4 nm. When thethickness of the Ti layer is less than 1 nm, the layer cannot functionadequately as a seed layer, and when the thickness is greater than 4 nm,growth of the PZT crystal is stopped at the boundary with the Ti layer,and there is a possibility that the crystal will be discontinuous andthat the layers will separate from each other. The Ti layer is morepreferably given a thickness of about 2 nm.

Second Step of Forming Piezoelectric Film (S5)

[0111] Next, a second step is conducted in which a piezoelectric film ofthe second layer is formed on the first piezoelectric film layer 43 a.In the second step, the step of annealing the piezoelectric precursorfilm by the same method as in the first step is repeated (for example,five times) until the piezoelectric film achieves the desired thickness,yielding a piezoelectric film 43 with a total thickness of 1.2 μm. Inparticular, the piezoelectric material of the second layer formed in thesecond step is formed into a layer with a thickness greater than that ofthe first layer formed in the above-mentioned first step (for example,between 0.1 μm and 0.3 μm).

[0112] Since the piezoelectric film from the second step is formed onthe first piezoelectric film layer 43 a from the above-mentioned firststep, the portion of the piezoelectric film 43 on the bottom electrode42 consists of a total of six layers, while a total of five layers makeup the portion formed on the exposed area of the ZrO₂ film 32 from whichthe first piezoelectric film layer 43 a and the bottom electrode 42 havebeen removed by patterning. Thus, within the piezoelectric film 43formed by the manufacturing method of the present embodiment, theportion formed on the bottom electrode 42 remaining from patterning ischaracterized by having a greater number of layers than the portionformed on the diaphragm film 30.

[0113] According to the present embodiment, the bottom electrode 42 hasalready been oxidized, diffused, and increased in overall thickness byannealing in the above-mentioned first step for forming a piezoelectricfilm, so the thickness of the bottom electrode does not increase anyfurther in the second step for forming a piezoelectric film.Consequently, the thickness of the bottom electrode 42 remains uniform,and the piezoelectric film 43 near the patterning boundaries of thebottom electrode 42 does not crack, nor does the crystal becomesdiscontinuous in the directions along with the film plane due tovariations in thickness of the bottom electrode 42.

[0114] As in the first embodiment, the portion of the piezoelectric film43 on the bottom electrode 42 is affected by the first (bottom) layer 43a of the piezoelectric film, a fine crystal with a low lattice constantis obtained, and a piezoelectric film is formed with a 100 plane degreeof orientation of 80%, as measured by wide-angle X-ray diffraction. Theportion formed on the exposed area of the ZrO₂ film 32 from which thebottom electrode 42 has been removed by patterning is affected by theabove-mentioned Ti layer, causing the orientation to be predominantlyalong the 111 plane.

[0115] Furthermore, the thickness of the Ti layer formed following theabove-mentioned patterning step (S4) is set to 4 nm or less, whereby thecrystalline structure becomes continuous in the thickness directionbetween the first piezoelectric film layer 43 a formed in the first stepof forming a piezoelectric film, and the piezoelectric film formed inthe second step of forming a piezoelectric film. The layers are lesslikely to separate from each other, making it possible to obtain ahighly reliable piezoelectric film 43.

Step of Forming Top Electrode (S6)

[0116] A top electrode 44 is formed on the piezoelectric film 43 byelectron beam vapor deposition or sputtering. The top electrode 44 isformed in a thickness of 50 nm using platinum (Pt), iridium (Ir), orother metals.

Step of Removing the Top Electrode and the Piezoelectric Film (S7)

[0117] The piezoelectric film 43 and the top electrode 44 are patternedinto a specific shape of a piezoelectric element. Specifically, afterthe top electrode 44 has been spin-coated with a resist, patterning isperformed by exposure or development at the location at which thepressure chamber is to be formed. The top electrode 44 and thepiezoelectric film 43 are etched by ion milling or the like with theremaining resist as a mask. A piezoelectric element 40 is formed by thestep described above.

Step for Forming Strip Electrode (S8)

[0118] Next, a strip electrode 46 is formed for ensuring conductivitybetween the top electrode 44 and the wiring bottom electrode 42 a. Ametal of low stiffness and electrical resistance is preferably used asthe material for the strip electrode 46. Aluminum, copper, or the likeare also suitable. The strip electrode 46 is formed in a thickness ofabout 0.2 μm, and is then patterned such that a conductive sectionremains between the top electrode and the wiring bottom electrode.

Step for Forming Pressure Chamber (S9)

[0119] Next, anisotropic etching, parallel-plate reactive ion etching,or any other types of anisotropic etching featuring an active gas isperformed on the surface of the pressure chamber substrate 20 oppositeof which the piezoelectric element 40 is formed, yielding a pressurechamber 21. The remaining portion that was not dry-etched forms the sidewall 22.

Step of Bonding the Nozzle Plate (S110)

[0120] Finally, a nozzle plate 10 is bonded with an adhesive agent tothe etched pressure chamber substrate 20. During bonding, each nozzle 11is positioned so as to be disposed in the spaces of the pressurechambers 21. The pressure chamber substrate 20, to which the nozzleplate 10 is bonded, is attached to the case (not shown), completing aninkjet recording head 1.

Other Modifications

[0121] The present invention can be modified and used in a variety ofways that do not depend on the above-mentioned embodiments. For example,the piezoelectric element manufactured in the present invention can beused not only in the above-mentioned piezoelectric element of an inkjetrecording head, but also in nonvolatile semiconductor storage devices,thin film condensers, pyroelectric detectors, sensors, surface acousticwave optical waveguides, optical storage devices, spatial lightmodulators, ferroelectric devices such as frequency doublers for diodelasers, dielectric devices, pyroelectric devices, piezoelectric devices,and electro-optic devices.

[0122] In addition to being adapted to a head for ejecting ink used inan inkjet recording apparatus, the liquid ejecting head of the presentinvention can also be adapted to various heads for injecting liquid,such as heads for ejecting liquids that contain the color materials usedin the manufacture of color filters for liquid displays and the like,heads for ejecting liquids that contain the electrode materials used inthe formation of electrodes such as organic EL displays or FED (fieldemission displays), and heads for ejecting liquids that contain thebiological material used in the manufacture of biochips.

[0123] According to the present invention, using the above-mentionedstructure makes it possible to obtain a highly reliable piezoelectricthin film element with superior piezoelectric properties in which thecondition of the crystal of the piezoelectric thin film is appropriatelycontrolled, and a manufacturing method thereof, as well as a liquidejecting head and liquid ejecting apparatus that employ the same.

What is claimed is:
 1. A piezoelectric thin film element, comprising atop electrode, a bottom electrode, and a piezoelectric thin film formedbetween the top electrode and the bottom electrode, wherein thepiezoelectric thin film comprises a plurality of layers; wherein theplurality of layers comprises a first layer located nearest to thebottom electrode, and a second layer that is located nearer to the topelectrode than the first layer and that has a thickness greater thanthat of the first layer; wherein the bottom electrode is patterned in aspecific configuration on a diaphragm; wherein the piezoelectric thinfilm is formed both on the bottom electrode remained after thepatterning and on the diaphragm from which the bottom electrode has beenremoved; and wherein the portion of the piezoelectric thin film on thebottom electrode remained after the patterning has a greater number oflayers than the portion on the diaphragm from which the bottom electrodehas been removed.
 2. The piezoelectric thin film element according toclaim 1, wherein the thickness of the first layer is not less than 10 nmand not more than 100 nm.
 3. The piezoelectric thin film elementaccording to claim 1, wherein the thickness of the second layer is notless than 100 nm and not more than 300 nm.
 4. The piezoelectric thinfilm element according to claim 1, wherein the first layer is composedof a PZT crystal having a rhombohedral crystal structure and a latticeconstant of 4.070 Å or less.
 5. The piezoelectric thin film elementaccording to claim 4, wherein the PZT crystal is a crystal comprising asolid solution of any one of the following groups: lead titanate andlead zirconate; lead titanate, lead zirconate and lead magnesiumniobate; lead titanate, lead zirconate and lead zincate niobate; or leadtitanate, lead zirconate and lead nickelate niobate.
 6. Thepiezoelectric thin film element according to claim 4, wherein a degreeof orientation in (100) plane of the PZT crystal is 70% or greater inthe thickness direction of the piezoelectric thin film.
 7. A liquidejecting head, comprising the piezoelectric thin film element accordingto claim 1 as a piezoelectric actuator for ejecting liquid.
 8. A liquidejecting apparatus, comprising the liquid ejecting head according toclaim
 7. 9. A method of manufacturing a piezoelectric thin film element,comprising: a step of forming a bottom electrode on a substrate; a stepof forming a piezoelectric thin film on the bottom electrode by asol-gel process; and a step of forming a top electrode on thepiezoelectric thin film; wherein said step of forming the piezoelectricthin film comprises: (a) a step of applying a sol onto the bottomelectrode and then performing drying and pyrolyzing to form a firstprecursor layer; (b) a step of annealing the first precursor layer byheating from the substrate side to form a first layer; (c) a step ofapplying the sol onto the first layer and then performing drying andpyrolyzing to form a second precursor layer; and (d) a step of annealingthe second precursor layer by heating from the substrate side to form asecond layer whose thickness is greater than that of the first layer.10. The method of manufacturing a piezoelectric thin film elementaccording to claim 9, wherein the second precursor layer is formed byapplying the sol onto the first layer and performing drying andpyrolyzing, and then again applying the sol thereon and performingdrying and pyrolyzing.
 11. The method of manufacturing a piezoelectricthin film element according to claim 9, further comprising a step offorming a Ti thin film on the bottom electrode, wherein the firstprecursor layer is formed by applying the sol to the bottom electrodevia the Ti thin film and then performing drying and pyrolyzing.
 12. Themethod of manufacturing a piezoelectric thin film element according toclaim 9, wherein the step of forming the piezoelectric thin film furthercomprises a step of patterning the first layer and the bottom electrodeafter forming the first layer and before forming the second precursorlayer; and wherein the second precursor layer is formed by applying thesol both onto the first layer remained after the patterning and onto thesubstrate from which the bottom electrode has been removed.
 13. Themethod of manufacturing a piezoelectric thin film element according toclaim 12, further comprising a step of forming a Ti thin film with athickness of not less than 1 nm and not more than 4 nm on the patternedfirst layer before forming the second precursor layer.
 14. A method ofmanufacturing a liquid ejecting head comprising a piezoelectric thinfilm element obtained by the method according to claim 9, comprising: astep of etching the substrate to form a pressure chamber; and a step offorming a nozzle plate for covering the pressure chamber.